1. Field of the Invention
This invention generally relates to a rear derailleur for a bicycle. More specifically, the present invention relates to an adjusting mechanism for adjusting the position of the chain guide in an axial direction with respect to a multistage sprocket assembly of the bicycle.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle as well as the frame of the bicycle. One component that has been extensively redesigned is the drive train of the bicycle.
Most of today's bicycles are multi-speed bicycles that allow the rider to select the appropriate gear ratio to suit the particular riding conditions encountered during the bicycle ride. One of the most popular types of gearing assemblies for multi-speed bicycles utilize a chain extending between a set of front sprockets mounted for rotation with the pedals and a set of rear sprockets mounted on the rear hub of the rear bicycle wheel for rotation therewith. Two derailleurs are typically used to move the chain between the sprockets or gears. Generally, most derailleurs (front or rear derailleurs) include a fixed or base member secured to a bicycle frame, and a movable member with a chain guide that is supported for movement relative to the fixed or base member by a linkage assembly. The chain guide has a pair of guide plates that form a chain receiving slot for contacting and moving a chain between the sprockets.
In the case of a rear derailleur, the chain guide has a pair of pulleys that are rotatably mounted between the guide plates. Also the base member of a rear derailleur is supported swingably to the bicycle frame through a horizontal shaft or axle, and the chain guide is swingably mounted to the movable member through a horizontal shaft or axle. A spring is interposed between the movable member and the chain guide for applying tension to the chain guide. The base member is fixed to a fork end of the bicycle frame, with the chain guide being disposed radially outwardly of the multistage sprocket assembly.
When the rider operates the shift operating device of the front derailleur shifting mechanism, the operating conduit or cable pulls the chain guide of the front derailleur such that the chain is moved outwardly from one gear or sprocket to the next gear or sprocket, or releases the front derailleur such that the chain is moved inwardly from one gear or sprocket to the next gear or sprocket. Likewise, when the rider operates the shift operating device of the rear derailleur shifting mechanism, the operating conduit or cable pulls the rear derailleur such that it moves the chain inwardly/outwardly from one gear or sprocket to the next gear or sprocket, or releases the rear derailleur such that it moves the chain outwardly/inwardly from one gear or sprocket to the next gear or sprocket. Typically, there are top-normal and low-normal type rear derailleurs, which are normally biased in outward and inward directions, respectively. Thus, while the front derailleur will move inwardly towards the center of the bicycle when its operating conduit or able is released, the rear derailleur will move outwardly or inwardly relative the center of the bicycle when its operating conduit or able is released, depending on if the rear derailleur is a top-normal or low-normal type.
The conventional derailleur which includes a chain guide capable of being adjusted in its axial position with respect to the multistage sprocket assembly is well-known as disclosed in U.S. Pat. No. 4,850,940 to Nagano and assigned to Shimano, Inc. Specifically, Shimano's prior U.S. Pat. No. 4,850,940 shows an adjusting mechanism for a chain guide which has a housing or movable member non-rotatably mounted on a tubular member via an adjusting screw. The tubular member is coupled to the chain guide via a fixing pin and bushing. A spring is disposed inside the tubular member to rotationally bias the tubular member and housing. The housing has an outer cylindrical portion that is slidable on the tubular member. The housing is not coupled to the fixing pin. Because the outer cylindrical portion is sized to slide on the tubular member and the housing is not coupled to the fixing pin, some play or looseness exists between these members. Also, due to this looseness, the housing can vibrate on the tubular member. Such vibrations can cause the adjusting screw to rotate undesirably. Such rotation of the adjusting screw can allow the chain guide to be out of alignment with the free wheel sprockets.
In view of the above, there exists a need for derailleur with an adjusting mechanism which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.